This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/JP99/00741 which has an International filing date of Feb. 19, 1999, which designated the United States of America.
The present invention relates to a photosensitive resin composition, more particularly to a photosensitive resin composition which is thermally stable, causes no improper development or discoloration with the lapse of time, and has excellent storage stability.
xe2x80x9cPhotosensitive resinxe2x80x9d referred to in the present invention is such a resin that a photopolymerization initiator contained therein generates a radical on receiving energy such as light or electron beam, allowing a radical crosslinking reaction to take place and selectively proceed at the light-irradiated portion to cause a change of solubility or dispersibility of the resin in solvents or a change of mechanical strength of the resin.
These resins generally contain an unsaturated compound and a photopolymerization initiator and are converted to polymeric resins after polymerization. In actual use of such resins, by taking advantage of the above property, the light-irradiated portion and the non-irradiated portion are treated with a developing solution (generally a solvent or an aqueous surfactant-containing solution) to remove the non-polymerized portion. (This treatment is hereinafter called development.)
These resins are thermally unstable because of their high reactivity. For instance, in case an article containing this type of resin is produced by a process requiring a high-temperature treatment, or is kept in storage for a long time, a radical crosslinking reaction takes place and proceeds in the resin throughout, even at the portion where it is desired to selectively prevent the polymerization from taking place, making it unable to perform normal development. In order to avoid such unfavorable phenomenon, various ideas have been proposed, such as lowering the treating temperature in the process or lowering the storage temperature. It has also been attempted to add a heat stabilizer to the resin to thereby maintain stability.
For instance, JP-A-62-95310 proposes use of hindered phenols (sterically hindered monophenols) or their thio-compounds.
However, the stabilizers which have so far been disclosed to be used for photosensitive resins and the like are unsatisfactory in their thermal stabilization effect. Some of those stabilizers are raised in their effect as their content is increased, but such stabilizers, in use, are reduced in sensitivity and prone to become substantially unserviceable, and are also subject to restrictions in relation to the process or compounding with the photosensitive resin.
It is also common practice to further contain a thermoplastic elastomer in a stabilizer-containing photosensitive resin composition for improving handling qualities of the composition. However, incorporation of a thermoplastic elastomer, which in itself is high in molecular weight, is liable to cause improper development.
The object of the present invention is to provide a photosensitive resin composition having high photopolymerization reactivity and thermal stability.
As a result of extensive studies for solving said problems in the prior art, the present inventors found that use of bis(3,5-di-t-butyl-4-hydroxybenzyl) sulfide (hereinafter referred to as BBHS in some cases) as a stabilizer produces a surprising stabilizing effect specifically for photosensitive resins, and further, additional use of 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-alkylphenyl acrylate (hereinafter referred to as BBHMAA in some cases) in combination with BBHS provides further improvement of the stabilizing effect, and that especially in a system containing a thermoplastic elastomer, the composition is made even more stable by containing a specific phosphorus compound in the composition. The present invention has been attained on the basis of the above finding.
Thus, the present invention provides:
(1) A photosensitive resin composition containing bis(3,5-di-t-butyl-4-hydoxybenzyl) sulfide.
(2) A photosensitive resin composition described in (1) above, also containing 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-alkylphenyl acrylate.
(3) A photosensitive resin composition described in (1) or (2) above, further containing a thermoplastic elastomer and at least one phosphorus compound selected from the group consisting of monoisodecyl phosphate, monomethyl acid phosphate, dimethyl acid phosphate, mono(2-(meth)acryloyloxyethyl) acid phosphate, bis(2-(meth)acryloyloxyethyl) acid phosphate, tri(2-(meth)acryloyloxy-ethyl) acid phosphate and tetrakis(2,4-di-t-butylphenyl)-4,4xe2x80x2-biphenylene diphosphonate.
The photosensitive resin compositions contain an unsaturated compound and a photopolymerization initiator, and other substances such as polymer, plasticizer, colorant, etc., which are added as required according to the purpose of use. For mixing these substances, suitable methods can be employed, such as melting the solid components in an extruder and injecting the liquid components thereinto, or mixing together all of the substances in a Banbury mixer or a kneader.
BBHMAA used in the present invention is a compound represented by the following structural formula: 
wherein R1 and R2 both represent an alkyl group. Because of high stabilizing effect, a compound of the above formula wherein both of R1 and R2 are methyl group (this compound 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate being hereinafter abbreviated as BBHMMA in some cases) is preferably used.
The content of the stabilizer BBHS is 0.01 to 5 parts by weight, preferably 0.1 to 0.9 parts by weight, per 100 parts by weight of the composition. The content of BBHMAA is 0 to 5 parts by weight, preferably 0.01 to 5 parts by weight, per 100 parts by weight of the composition, more preferably equal to the content of BBHS. If the content of these stabilizers is below the above-defined ranges, the produced effect falls short of being satisfactory. If their content exceeds the above-defined ranges, there can not be obtained a greater effect than a certain level, and in this case, sensitivity of the composition may be lower.
Especially in the system containing a thermoplastic elastomer, additional incorporation of a phosphorus compound such as mentioned in (3) above is conducive to further promotion of the thermal stabilizing effect to improve the developing characteristics of the composition.
The stabilizer according to the present invention can be contained in the composition by a known method. For example, the stabilizer may be dissolved or uniformly dispersed in the liquid component so that it may be injected with the liquid component. In case the stabilizer is liquid, it may be injected separately from the liquid component, and if the stabilizer is solid, it may be supplied together with the solid component. Generally, the stabilizer is added before the process temperature rises up, but in order to enhance keeping quality of the final product, the stabilizer may be contained in the product by a specific method such as by impregnation.
As the unsaturated compound contained in the photosensitive resin composition, any compound can be used so far as it has a double-bond in the molecule and is liquid or solid at the working temperature. Preferably, the acrylic acid or methacrylic acid compounds having high reactivity and also high compatibility with various compounds are used, and the esters of acrylic or methacrylic acids are more preferably used because of lower toxicity and smaller metal corrosiveness.
Examples of such compounds include alkyl (meth)acrylate, cycloalkyl (meth)acrylate, halogenated alkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, hydroxyalkyl (meth)acrylate, aminoalkyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, glycidyl (meth)acrylate, benzyl (meth)acrylate, phenoxy (meth)acrylate, alkylene glycol di(meth)acrylate, polyoxyalkylene glycol di(meth)acrylate, and alkylpolyol poly(meth)acrylate. To be more specific, they include diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, hexamethylene di(meth)acrylate, nonamethylene di(meth)acrylate, polybutadiene diacrylate, polyisoprene diacrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 1-(meth)acryloyloxy-2-hydroxy-3-phenoxypropane, phenoxyethyl (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, bis-(meth)acryloyloxyethylhydroxyethyl isocyanurate, and tris(meth)acryloyloxyethyl isocyanurate,
In the specification, xe2x80x9c(meth)acrylatexe2x80x9d denotes xe2x80x9cacrylate or methacrylatexe2x80x9d, and xe2x80x9c(meth)acryloylxe2x80x9d denotes xe2x80x9cacryloyl or methacryloylxe2x80x9d.
The content of the unsaturated compound is 1 to 95% by weight, preferably 3 to 80% by weight, based on the whole photosensitive resin composition. Too high of a content induces an unnecessary rise of temperature or chain reaction by polymerization heat in the reaction, causing advancement of crosslinking even to the area where light does not reach. Too low of a content is causative of a slow reaction or insufficiency of the difference in solubility in the solvent or mechanical strength from the unreacted portion, making it difficult to accomplish accurate development.
Various known types of photopolymerization initiators can be used in the present invention although various organic carbonyl compounds, especially aromatic carbonyl compounds are preferred. Examples of such compounds are shown below.
1) Benzoin and its derivatives represented by the formula (1), such as benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether and benzoin isobutyl ether. 
wherein R1 is a hydrogen atom or an alkyl group such as methyl, ethyl, isopropyl or isobutyl.
2) Phenyl ketones represented by the formula (2), such as 2,2-dimethoxy-2-phenylacetophenone. 
wherein R2, R3, R4 and R5 may be identical or different and represent independently a hydrogen atom, a halogen atom, an alkyl group, an alkoxyl group, a hydroxyl group, a phenyl group, an alkylthio group, a morpholino group or the like.
3) Benzophenone and its derivatives represented by the formula (3), such as methyl-O-benzoyl benzoate. 
wherein R6 and R7 may be identical or different and represent independently a hydrogen atom, an alkyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, an alkylthio group, an amino group or the like.
These photopolymerization initiators may be used either singly or as a combination of two or more.
The content of the photopolymerization initiator is not less than 0.1 part by weight and not more than 30 parts by weight per 100 parts by weight of the photosensitive resin composition. If the content of the photopolymerization initiator is less than 0.1 part by weight, the photo-setting properties of the whole composition prove to be defective, while if the content exceeds 30 parts by weight, transmission of light may be hindered to induce photo-setting of the surface alone.
The thermoplastic elastomers usable in the present invention include thermoplastic elastomer-like block copolymers such as styrene-butadiene block copolymer, styrene-isoprene block copolymer and styrene-butadiene-acrylic ester copolymer; polyurethane-based thermoplastic elastomers, polyester-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.
These thermoplastic elastomers may contain as a plasticizer an unsaturated diene compound such as liquid polybutadiene, liquid polyisoprene or a modified unsaturated diene compound such as maleate-modified polybutadiene, acrylate-modified polybutadiene, epoxymodified polybutadiene, for the purpose of imparting softness to the elastomers.
The content of the thermoplastic elastomer is 0 to 95% by weight, preferably 5 to 90% by weight, based on the whole resin composition. Too high elastomer content may cause an unnecessary rise of viscosity of the photosensitive resin composition, while too low of a content may lead to unsatisfactory mechanical properties of the photo-set product, making it fragile.
The phosphorus compounds that can be used in the present invention for the purpose of improving stability include, for example, monoisodecyl phosphate, monomethyl acid phosphate, dimethyl acid phosphate, mono(2-(meth)-acryloyloxyethyl) acid phosphate, bis(2-(meth)acryloyloxy-ethyl) acid phosphate, tri(2-(meth)acryloyloxyethyl) acid phosphate, and tetrakis(2,4-t-butylphenyl)-4,4xe2x80x2-biphenylene diphosphonate. These compounds may be used either singly or as a combination of two or more.
The content of such a phosphorus compound(s) is 0.01 to 5 parts, preferably 0.05 to 1 part, per 100 parts by weight of the photosensitive resin composition. Too small of a content of this compound cannot derive its effect sufficiently. Use of this compound in an excess amount does not provide an extra effect and rather causes a drop of turbidity to give an adverse effect to the reproducibility of a negative at the time of photo-setting.
Quite surprisingly, use of such a phosphorus compound significantly improves the developing performance. Specifically, by use of an appropriate amount of this compound, it is possible to reduce the time required for developing an area of 1 mm to ⅓ or less.
In the photosensitive resin composition of the present invention, the conventional additives such as pigment, dye, microgel, surfactant, etc., may be contained within limits not prejudicial to the photosensitivity, developing performance and physical properties of the composition.
The present invention will be described in further detail with reference to the embodiments thereof.
1) Gelation Test
A composition was prepared by blending 5 parts by weight of a polybutadiene diacrylate (BAC-45 produced by Osaka Yuki Kagaku KK), 1 part by weight of an aliphatic diacrylate (C-2000 produced by THERTMER), 2 parts by weight of dioctyl fumarate and 10 parts by weight of a maleate-modified polybutadiene (MM-1000-80 produced by Nippon Sekiyu Kagaku KK) as the unsaturated compounds used in Referential Example 1(2) described below, 2 parts by weight of 2,2-dimethoxyphenylacetophenone as photopolymerization initiator, and 5 parts by weight of the sulfonic group-containing polyurethane (polymer moiety of the photosensitive resin composition) obtained in Referential Example 1(1) described below for preventing separation of the unsaturated compounds at high temperatures. Then a predetermined amount of a stabilizer was dissolved in the composition. This sample was put into a test tube with a glass rod placed therein, and left in a nitrogen atmosphere of 140xc2x0 C. The test tube was observed every hour, and the time required till the glass rod became immobile was decided as gelation time.
2) Storage Stability Test
The photosensitive resin compositions prepared by using as a main constituent the composition obtained in Referential Example 1(2) described below and adding the stabilizers as shown in Table 2 were kept under atmospheric pressure at the temperatures of 20xc2x0 C. and 40xc2x0 C., and their developing behavior (developing speed) with time was observed. Development was conducted in an aqueous treating solution, and the time required till the time for developing of an area of 1 mm became doubled, or more, was expressed as a development failure time. Measurement was made at the points of passage of one month, 3 months, 6 months and 12 months after the start of the test. In practical use, it is desirable that the composition is stable for more than half a year, preferably more than 2 years at 20xc2x0 C.
As the aqueous treating solution, a mixed solution of 2 parts by weight of sodium borate, 2 parts by weight of octylphenoxypolyoxyethylene ether and 100 parts by weight of water was used.
3) Accelerated Storage Stability Test
The photosensitive resin composition was kept at 90xc2x0 C., 110xc2x0 C. and 140xc2x0 C. and its developing behavior (developing speed) with test was observed. The time required till the time for developing of an area of 1 mm became doubled or more was expressed as a development failure time.
Since temperature dependency of storage stability conforms to the Arrhenius"" law, this test is designed to we predict long-time storage stability in a short time by conducting the test at high temperatures. The desirable practical level in this test is over the level of 72 hours at 90xc2x0 C., and this level is equivalent to storage stability of two years or more.
4) Determination of Sensitivity
The photosensitive resin composition was exposed to light via its PET film side having an adhesive layer, and after developing the uncured resin with an aqueous treating solution, thickness of the cured portion was measured and sensitivity was determined from this thickness. The sample which suffered 20% or more decrease of thickness as compared with Comparative Example 1 was marked xc3x97, the sample which was the same in thickness as or suffered less than 20% decrease of thickness compared with Comparative Example 1 was marked ◯, and the sample which became thicker than Comparative Example 1 was marked ⊚. A near ultraviolet lamp having a peak wavelength at 370 nm was used for exposure. The developing solution used in the test was a mixture of 2 parts by weight of sodium borate, 2 parts by weight of octylphenoxypolyoxyethylene ether and 100 parts by weight of water.
(1) Synthesis of Sulfonic Acid Group-containing Polyurethane
To a 1,000 ml separable flask provided with a stirrer, a nitrogen inlet port and an outlet pipe, 296 g of sodium sulfoisophthalate dimethyl ester, 310 g of ethylene glycol, 0.43 g of N,Nxe2x80x2-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamylamide) (IRGANOX 1098 produced by CibaGeigy Corp.) and 0.43 g of zinc acetate were supplied and reacted in a nitrogen atmosphere at 200xc2x0 C. for 5 hours, and then unreacted ethylene glycol was distilled away under reduced pressure to obtain a light-yellow sulfonic acid group-containing polyester diol having a hydroxyl group at the terminal. The number-average molecular weight of this product was determined to be 492 from measurement of hydroxyl number.
To a 3,000 ml separable flask provided with a stirrer, a nitrogen inlet port and an outlet pipe, 39.9 g of said sulfonic acid group-containing polyester diol, 377.7 g of a polyisoprene diol having a number-average molecular weight of 2,439 and possessing hydroxyl groups at both terminals (produced by Idemitsu Petrochemical Co., Ltd.) and 1.4 g of octylated diphenylamine (NOCRAC AD produced by Ouchi Shinko Kagaku KK) were supplied, and then 1,000 g of dimethylamide and 1,000 g of 2-chlorotoluene were added to form a homogeneous solution at 110xc2x0 C.
Then 0.11 g of dibutyltin dilaurate and 0.34 g of stannous octoate were further added, and the mixture was reacted at 110xc2x0 C. for 3 hours while dropping 43.1 g of xylylene diisocyanate, after which dimethylacetamide and 2-chlorotoluene were distilled away under reduced pressure to obtain a homogeneous and transparent sulfonic acid group-containing polyurethane.
(2) Preparation of Photosensitive Resin Composition
49.5 g of the sulfonic acid group-containing polyurethane obtained in (1) above was kneaded with 20 g of a styrene-isoprene block copolymer (CALIFLEX TR1107 produced by Shell Chemical Co.), 2 g of sodium lauryl-benzenesulfonate, 5 g of a polybutadiene diacrylate (BAC-45 produced by Osaka Yuki Kagaku KK), 1 g of an aliphatic diacrylate (C-2000 produced by THERTOMER), 2 g of dioctyl fumarate, 2 g of 2,2-dimethoxyphenylacetophenone, 10 g of a maleate-modified polybutadiene (MM-1000-80 produced by Nippon Sekiyu Kagaku KK) and 7.5 g of N-ethyltoluene-sulfonamide by a press kneader in a nitrogen atmosphere at 150xc2x0 C. to obtain a homogeneous and transparent photosensitive resin composition.